Heh Jeff's gonna hate me for this but I couldn't resist it.

400,000 rows in 15 seconds:

IF OBJECT_ID('tempdb..#tempstore') IS NOT NULL DROP TABLE #tempstore;

CREATE TABLE #tempstore (acct_nbr INT,

ckid INT,

stat varchar(10),

Grp int);

INSERT INTO #tempstore (acct_nbr, ckid, stat)

SELECT 1, 101 ,'Open' UNION ALL

SELECT 1, 102 ,'Open' UNION ALL

SELECT 1, 103 ,'Open' UNION ALL

SELECT 1, 104 ,'Void' UNION ALL

SELECT 1, 105 ,'Void' UNION ALL

SELECT 1, 106 ,'Open' UNION ALL

SELECT 1, 107 ,'Open' UNION ALL

SELECT 1, 108 ,'Open' UNION ALL

SELECT 1, 109 ,'Void' UNION ALL

SELECT 1, 110 ,'Open' UNION ALL

SELECT 2, 101 ,'Open' UNION ALL

SELECT 2, 102 ,'Open' UNION ALL

SELECT 2, 103 ,'Open' UNION ALL

SELECT 2, 104 ,'Void' UNION ALL

SELECT 3, 105 ,'Void' UNION ALL

SELECT 3, 106 ,'Open' UNION ALL

SELECT 3, 107 ,'Open' UNION ALL

SELECT 4, 108 ,'Open' UNION ALL

SELECT 4, 109 ,'Void' UNION ALL

SELECT 4, 110 ,'Open';

-- 400,000 rows of data

IF OBJECT_ID('tempdb..#temp') IS NOT NULL DROP TABLE #temp;

CREATE TABLE #temp (acct_nbr INT,

ckid INT,

stat varchar(10),

Grp int);

INSERT INTO #temp (acct_nbr, ckid, stat)

SELECT acct_nbr+(4*n), ckid+(20*n), stat

FROM #tempstore

CROSS JOIN (SELECT TOP 20000 [n] = ROW_NUMBER() OVER(ORDER BY a.[name])-1 FROM master.dbo.syscolumns a, master.dbo.syscolumns b) n

-- copy our data to a working table

SELECT rn = ROW_NUMBER() OVER (ORDER BY acct_nbr, ckid),

acct_nbr, ckid, stat

INTO #Workings

FROM #temp

ORDER BY acct_nbr, ckid

CREATE UNIQUE CLUSTERED INDEX CIrn ON #Workings ([rn] ASC)

-- get the results

;WITH Calculator AS (

SELECT rn, acct_nbr, ckid, stat, NewGroup = CAST(1 AS INT)

FROM #Workings WHERE rn = 1

UNION ALL

SELECT w.rn, w.acct_nbr, w.ckid, w.stat,

NewGroup = CASE

WHEN w.acct_nbr <> c.acct_nbr THEN 1

WHEN w.stat <> c.stat THEN c.NewGroup + 1

ELSE c.NewGroup END

FROM #Workings w

INNER JOIN Calculator c ON c.rn+1 = w.rn)

SELECT acct_nbr, ckid, stat, NewGroup

FROM Calculator

OPTION( MAXRECURSION 0)

-- 400,000 rows: 15 seconds